The more dour image, while useful for an aspiring chancellor, is not necessarily seen as the best asset for someone hoping to spearhead a party's general election campaign.

Fortunately for the man considered by many as the PM-in-waiting, the nine years since reaching Downing Street have seen a steady transformation in Mr Brown's image from a rather studious bachelor to happy family man.

There is no doubt Mr Brown cultivated his sober, earnest image in the early years of his political career, at a time when Labour was attempting to shake off its reputation for economic incompetence.

With his close-knit group of friends and advisers, such as Ed Balls and Geoffrey Robinson, Mr Brown could afford to be more relaxed.

But as shadow chancellor, he wanted to be seen as a model of rectitude and prudence, a fearsome guardian of the purse strings, unafraid of making tough decisions.

Devotion to duty

During the 1997 election campaign Gordon Brown was said to have worked an average of 18 hours a day, six days a week - after running on a treadmill for an hour each morning.

That devotion to duty was underlined by a comment from his former girlfriend of five years, Princess Marguerite of Romania, the eldest daughter of ex-King Michael of Romania, who said a relationship with him was "politics, politics, politics".

Our baby is wonderful, he's beautiful, he's really full of energy and I think he's going to keep me awake for quite a number of days, weeks and months

Gordon Brown on baby John

His continued bachelor status had, meanwhile, sparked rumours he was gay - something he politely but firmly denied when asked about it by Sue Lawley on BBC Radio 4's Desert Island Discs.

He had in fact been seeing PR executive Sarah Macaulay at the time, but chose not to draw attention to their relationship.

And this low-key approach continued when the couple got married in 2000, after going out with each other for six years.

Mrs Brown

Their's was not a flashy, Hello magazine occasion. Instead the couple wed quietly in Fife, Scotland, with close family and friends, before jetting off for a honeymoon in Cape Cod.

Unlike Cherie Blair, who works under the professional moniker of Booth, Sarah told guests she had decided to drop her maiden name, wanting instead to be known as Mrs Brown.

The Browns' wedding was a quiet ceremony in Scotland

On 28 December, 2001 the couple became parents, with the premature birth by Caesarean section of Jennifer Jane, weighing 2lb 4oz.

Overnight, Mr Brown's serious exterior was replaced by big smiles and joy as he told the world his daughter was the "most beautiful in the world".

But tragedy struck just 10 days later when the little girl suffered a brain haemorrhage and lost her fight for life in her parents' arms at Edinburgh Royal Infirmary.

The image of a heartbroken chancellor, who described Jennifer as an "inspiration", touched the nation.

That meant the Browns' joy was felt all the more widely when in October 2003, the couple had a son, John - named after his grandfather - weighing 8lb 1oz.

Impressive record

Dressed down in a white open-necked shirt under a dark jumper, he could not contain his happiness as he presented the little boy to waiting photographers in a multi-coloured sleep suit.

"Our baby is wonderful, he's beautiful, he's really full of energy and I think he's going to keep me awake for quite a number of days, weeks and months," he said.

Gordon and Sarah Brown with 'beautiful' baby John

In July 2006, the couple had a second son, 8lb James Fraser, prompting the normally reserved chancellor to exclaim: "I just love being a dad, it's great fun - there's nothing more important."

Four months later, Mr Brown's spokesman confirmed a newspaper report that young Fraser, as he is known, had been diagnosed with cystic fibrosis.

The Browns received numerous messages of support after the news about Fraser, who was said to be "fit, healthy and making all the progress that you would expect any little boy to make".

The chancellor's spokesman said "they are confident that the advice and treatments available, including proper exercise and, later, sporting activity will keep him fit and healthy".

"The NHS is doing a great job, and Gordon and Sarah are very optimistic that the advances being made in medicine will help him and many others, and they hope to be able to play their part in doing what they can to help others."

Open neck shirts

In politics, Mr Brown, now 55, has shown himself as a steady pair of hands with an impressive economic record - but he has always refused to wear the official "uniform" of coat tails and white bow tie when he gives his annual Mansion House address to the world's financial bigwigs, finding the "idea of wearing such formal dress ridiculous".

Over time, Mr Brown's image has, however, undergone a considerable makeover, taking him from a rather scruffy bachelor to groomed man about town.

He has, in the process, risked accusations he is chasing photo opportunities.

He faced flak during the World Cup this year after he declared himself a staunch supporter of England, even inviting reporters to his flat to watch one of the games with him.

This seemed to be part of a conscious effort to present a lighter, more approachable image - which has also seen his traditional dark suits, white shirts and red ties make way for a more casual look with chinos, open neck shirts and the occasional pink or purple tie.

Many credit this change of wardrobe to his wife's PR-expertise - or to his backroom team's efforts to present him as a modern world-leader-in-waiting.

It was certainly well timed after the election of the youthful David Cameron as Conservative leader.

The chancellor also smiles a lot more than he used to.

His teeth are noticeably whiter, which despite what he says, is generally seen as unlikely to be as a result of just "a few fillings".

He has been pictured in a flak jacket and open-necked shirt looking relaxed and striding from a helicopter in Basra on his surprise visit to Iraq earlier this month.

And unlike before, where little was known about the son of a Church of Scotland minister, no topic of conversation seems out of bounds.

Popular tastes

In political agenda terms he has embraced subjects such as Britishness, climate change, and world poverty campaign - which included hanging out with the likes of Angelina Jolie and rock stars such as Bono.

He has revealed he has a sense of humour, with his Christmas card this year done by well-known children's illustrator Axel Scheffler, of children reading books around a Christmas tree - with one lone child in a corner looking perplexed at a red dispatch box.

And in an interview earlier this year, he suggested that his son John has had the controversial MMR jab, something Tony Blair refuses to discuss on privacy grounds.

He was also happy to tell a magazine that his underwear comes from M&S, and was quoted as saying he likes to wake up to the sound of hip young band the Arctic Monkeys - although he later said his comments had been misreported.

He says he owns an iPod music player and is a fan of TV's X-Factor. He also disclosed his wife believes that if anyone was going to play him in a film, it should be Hollywood heart-throb George Clooney.

It is all quite a change from the man, widely expected to become prime minister, who was once mocked by opponents for talking warmly of "post neo-classical endogenous growth theory".